TW202106847A - Synthetic grinding stone - Google Patents

Abstract

A synthetic grinding stone for chemical mechanical grinding of a wafer W according to the present invention comprises: a polishing agent which is mainly composed of fumed silica that has a chemical mechanical grinding action on the wafer W, while having a particle diameter of less than 5 [mu]m; a spherical filler which is mainly composed of spherical silica gel that is formed of a material equal to the wafer W or a soft material, while having a particle diameter that is larger than the particle diameter of the polishing agent; and a resin binder which is mainly composed of a cellulose that integrally binds the polishing agent and the spherical filler with each other.

Description

Synthetic grindstone

Invention field The present invention relates to a synthetic grindstone used to grind the surface of a silicon wafer and other workpieces.

Background technique In the field of semiconductor manufacturing, the surface processing of the silicon wafer that constitutes the substrate of the semiconductor device generally involves the finishing of the wafer that has been sliced into the silicon single crystal ingot through several stages such as polishing step, etching step, and polishing step. Mirror surface. In the polishing step, dimensional accuracy and shape accuracy such as parallelism and flatness are obtained. Next, in the etching step, the processed deterioration layer generated in the polishing step is removed. Furthermore, in the polishing step, chemical mechanical polishing (hereinafter referred to as "CMP") is used to form a wafer with mirror-grade surface roughness while maintaining good shape accuracy. In addition, the same polishing step can also be used to remove the damage of the grinding process called back grinding in the subsequent step of the semiconductor.

The method used in recent years is to perform surface processing using dry chemical mechanical grinding (hereinafter referred to as "CMG") instead of the polishing step (for example, refer to Patent Document 1). In the CMG step, a synthetic grindstone in which an abrasive (abrasive grain) has been immobilized with a resin bond such as a hard resin is used. In addition, while rotating the wafer and the synthetic grindstone, the synthetic grindstone is pressed against the wafer (for example, refer to Patent Document 2). The protrusions on the wafer surface are heated, oxidized, and then become brittle and peel off by friction with the synthetic grindstone. In this way, only the convex part of the wafer will be ground and flattened.

When the main component of the synthetic grindstone is a silicon wafer, for example, oxides such as cerium oxide or silicon dioxide are used as abrasives. In addition to thermosetting resins such as phenol resins and epoxy resins, resin binders also use thermoplastic resins with high heat resistance.

Prior art literature Patent literature Patent Document 1: Japanese Patent No. 4573492 Patent Document 2: Japanese Patent Application Publication No. 2004-87912

Summary of the invention The problem to be solved by the invention The above-mentioned synthetic grindstone has the following problems. That is, if the CMG step is performed, the abrasive will drop little by little from the grinding surface of the synthetic grindstone on the workpiece, and the grinding surface will gradually become smooth. Therefore, the chance of contact between the resin bond and the workpiece on the polishing surface increases. As a result, the contact pressure between the abrasive and the workpiece is reduced, and the processing efficiency is significantly reduced. On the other hand, especially when the processing rate is increased When dry processing is performed for the purpose, the frictional heat will become too large, and there will be a problem of burns or scratches caused by being involved in the grinding sludge.

Therefore, the present invention was made in order to solve the above-mentioned problems, and its object is to provide a synthetic grindstone that can sufficiently maintain the contact pressure between the abrasive and the workpiece to maintain the processing efficiency even if the processing is continued, and The contact area between the resin bond and the workpiece is suppressed below a certain value, thereby preventing the quality of the workpiece surface from degrading and the generation of scratches.

Means to solve the problem The synthetic grindstone of this embodiment includes: an abrasive, which has a chemical-mechanical grinding effect on the aforementioned material to be cut, and has an average particle size of less than 5μm; a spherical filler with an average particle size larger than the foregoing abrasive; and a resin bond , It integrally combines the aforementioned abrasive and the aforementioned spherical filler.

Invention effect Even if the processing is continued, the contact pressure between the abrasive and the workpiece can be sufficiently maintained to maintain the processing efficiency, and the contact area between the resin bond and the workpiece can be suppressed below a certain value, thereby preventing the surface of the workpiece The quality is reduced and scratches are generated.

The form used to implement the invention Figures 1 to 4 show an embodiment of the present invention. In these figures, W denotes a silicon wafer (a workpiece) to be ground. As shown in FIG. 1, the CMG device 10 includes: a rotating platform mechanism 20 that supports a wafer W; and a grindstone support mechanism 30 that supports a synthetic grindstone 100 described later. The CMG device 10 constitutes a part of a wafer processing device. In the CMG device 10, the wafer W can be carried in and out by a transfer robot or the like.

The rotating platform mechanism 20 includes a platform motor 21 which is arranged on the ground; a platform shaft 22 which protrudes upward from the platform motor 21 and is arranged; and a platform 23 which is mounted on the upper end of the platform shaft 22. The stage 23 has a mechanism for holding the wafer W to be polished so as to be freely attachable and detachable. The holding mechanism includes, for example, a vacuum suction mechanism.

The grindstone support mechanism 30 is provided with a stand 31, which is arranged on the ground and a motor is housed inside; a vertical swing shaft 32, which is supported on the stand 31, and uses the motor in the stand 31 to move toward the arrow in Fig. 1 The arm part 33 is arranged at the upper end of the shaking shaft 32 and extends in the horizontal direction; and the grindstone driving mechanism 40 is arranged at the front end side of the arm part 33.

The grindstone drive mechanism 40 includes a rotation motor unit 41. The rotation motor unit 41 includes a rotation shaft 42 protruding downward. A ring-shaped wheel holding member 43 is attached to the front end of the rotating shaft 42. On the wheel holding member 43, as shown in FIG. 2, the ring-shaped synthetic grindstone 100 is installed so as to be freely attachable and detachable. When installing the synthetic grindstone 100, bolts are screwed into the screw holes already provided in the synthetic grindstone 100 from the wheel holding member 43 side to install.

As shown in Figure 3, the synthetic grindstone 100 is made of 0.2-50% by volume of abrasive 101, 20-60% by volume of spherical filler 102, and 3-25% by volume of resin bond 103 using the following volume ratios form. In addition, the shape of the spherical filler 102 is not necessarily limited to a spherical body, and if it is a block shape, it includes a little unevenness or deformation.

For the abrasive 101, fumed silica having a particle size of 20 nm or less is used, for example. In addition, the so-called particle diameter means the median diameter D50 under the equivalent diameter of the sphere. In addition, the particle size of the abrasive 101 is preferably less than 5 μm.

Here, although fumed silica having a particle size of 20 nm or less is used, the reason for setting the upper limit of the particle size of the abrasive 101 to be less than 5 μm will be described. That is, the primary particles in the state where the fine particles are dispersed in the liquid and the secondary particles in the state where the fine particles have been aggregated in the air or in the solid have very different particle sizes. For example, in the above fumed silica, the primary particles are 10-20nm, but the secondary particles are about 0.1-0.5μm. Therefore, when specifying the upper limit of the particle size of the abrasive, it is advisable to consider the mixing of primary particles and secondary particles, and specify the upper limit of the particle size of the secondary particles. On the other hand, in addition to fumed silica, fine particles also have various types (cerium oxide, chromium oxide, iron oxide, aluminum oxide, silicon carbide, etc.) as described later, which can be determined according to the size of their secondary particles. Upper limit.

In addition, when the particle size is a submicron particle of 1 μm or less, the volume ratio of the abrasive 101 may be 0.2 to 1%. The spherical filler 102 uses spherical silica gel with a particle diameter of 20 μm. In addition, spherical silica gel is a porous body of silica. As the resin binder 103, for example, a phenol resin or ethyl cellulose is used. If the synthetic grindstone 100 formed in this way is enlarged and displayed with an electron microscope, it will become as shown in FIG. 4.

The synthetic grindstone 100 is made by dissolving the abrasive 101, the spherical filler 102, and the resin binder 103 in the MEK (methyl ethyl ketone) solvent in the above ratio, and then drying in the atmosphere after stirring. The dried material is pulverized to form a powder, and the powder is filled in a mold, and formed by press molding at 180°C. The abrasive 101 and the resin bond 103 form the base material M, and the spherical filler 102 is dispersed in the base material M. In addition, it is also possible to adjust the bonding degree of the resin bonding agent 103, or to add finer particles or fibers with a smaller diameter than the abrasive 101 in order to improve the dispersibility of the tissue.

In addition, with respect to the wafer W having silicon as the main component, the abrasive 101 made of fumed silicon dioxide is equivalent to or softer than the wafer or its oxide. In addition, with respect to the abrasive 101, the spherical filler 102 made of spherical silicone is the same or soft as the wafer or its oxide. In addition, with respect to the abrasive 101, the resin binder 103 made of cellulose is homogeneous or soft.

In addition, the volume ratio in the synthetic grindstone 100 mentioned above is determined as follows. That is, if the abrasive 101 is less than 0.2% by volume, the processing efficiency is reduced, and if it is greater than 50% by volume, the molding of the grindstone becomes difficult. Therefore, the volume ratio of the abrasive 101 should be 0.2-50%.

In addition, when the spherical filler 102 is less than 20% by volume, there is a problem that the effect of preventing the smoothing of the grinding surface is weak. If the volume ratio of the spherical filler 102 is increased, the processing efficiency can be maintained at a high level, and at the same time, the effect of preventing the quality of the wafer W from deteriorating and the generation of scratches is large, so it is preferably 30% by volume or more. However, if it exceeds 60% by volume, it becomes difficult to shape the grindstone. Therefore, the volume ratio of the spherical filler 102 is preferably 20-60%, and it is more ideal if it is 50-60%.

Furthermore, if the ratio of the resin bond 103 is reduced, the processing efficiency is improved, but if it is less than 3% by volume, molding becomes difficult, and the wear rate of the synthetic grindstone 100 increases. If the resin bond 103 is more than 25% by volume, the degree of bonding of the grindstone is greatly increased, and abrasion during processing disappears. Therefore, even with the spherical filler described above, smoothing of the grinding surface is likely to occur. Therefore, the volume ratio of the resin bond 103 is preferably 3-25% by volume.

The synthetic grindstone 100 constructed in this way is installed in the CMG device 10, and the wafer W is ground as follows. That is, the synthetic grindstone 100 is mounted on the wheel holding member 43. Next, the wafer W is mounted on the platform 23 by the transfer robot.

Next, the platform motor 21 is driven to rotate the platform 23 in the direction of the arrow in FIG. 1. In addition, the rotation motor unit 41 is driven to rotate the wheel holding member 43 and the synthetic grindstone 100 in the direction of the arrow in FIG. 1. For example, the synthetic grindstone 100 is rotated at a peripheral speed of 600 m/min, while pressing against the wafer W side ^{with a processing pressure of 300 g/cm 2.} Furthermore, the rocking shaft 32 is rocked in the direction of the arrow in FIG. 1. With these linkages, the synthetic grindstone 100 and the wafer W will slide.

FIG. 3 shows the relationship between the synthetic grindstone 100 and the wafer W at this time. The average particle size of the spherical filler 102 is larger than that of the abrasive 101. Therefore, the synthetic grindstone 100 and the wafer W being processed are in contact almost through the apex of the spherical filler 102. That is, there is a spherical filler 102 between the base material M of the synthetic grindstone 100 and the wafer W. Therefore, the base material M and the wafer W do not directly contact, and a certain gap S is generated.

If the processing is started in a state where the spherical filler 102 is in contact with the wafer W, external force will act on the base material M. Under the continuous action of this external force, the resin bond 103 will relax, and the abrasive 101 will fall off the base material M. The free abrasive 101 is present on the processing interface in a state of being adsorbed on the spherical filler 102 in the gap between the synthetic grindstone 100 and the wafer W. Therefore, the polishing agent 101 and the wafer W during processing are almost in contact with each other through the apex of the spherical filler 102. Therefore, the actual contact area between the abrasive 101 and the wafer W will be greatly reduced, and the pressure at the processing point will increase. Therefore, grinding can be performed with high processing efficiency.

On the other hand, the gap S can promote the circulation of the air near the surface of the wafer W and the outside air, and the processed surface will be cooled. In addition, the sludge generated by the abrasive 101 is discharged from the wafer W to the outside through the gap S, and damage to the surface of the wafer W can be prevented. As a result, it is possible to prevent burns or scratches on the surface of the wafer W caused by frictional heat.

In this way, the synthetic grindstone 100 is used to grind the surface of the wafer W to be flat and have a predetermined surface roughness.

As described above, according to the synthetic grindstone 100 of this embodiment, even if the processing is continued, the contact pressure between the abrasive 101 and the wafer W can be sufficiently maintained to maintain the processing efficiency, and the direct contact between the resin bond 103 and the wafer W can be suppressed. Contact, thereby preventing the deterioration of the quality of the wafer W and the generation of scratches.

In addition, the material constituting the synthetic grindstone 100 is not limited to the above-mentioned materials. That is, as the abrasive 101, when the material to be cut is silicon, silicon dioxide or cerium oxide can be used, and when the material to be cut is sapphire, chromium oxide or iron oxide can be used. In addition, as an applicable abrasive, alumina and silicon carbide can also be used according to the type of material to be cut.

The spherical filler 102 can be silicon dioxide, carbon, silica gel, activated carbon, etc., which belong to these porous bodies. In addition, the hollow balloon used as a pore forming agent may break during processing and cause scratches, so it is not suitable.

In addition to thermosetting resins such as phenol resin and epoxy resin, the resin bonding agent 103 can also be applied to thermoplastic resins such as ethyl cellulose. In the case of a thermoplastic resin, it can be used as long as it has a high softening point of 120°C or higher and a low degree of elongation.

In addition, the present invention is not limited to the above-mentioned embodiment, and various modifications can be made without departing from the scope of the implementation stage. In addition, each of the embodiments can be appropriately combined and implemented, and in this case, a combined effect can be obtained. Furthermore, various inventions are included in the above-mentioned embodiment, and various inventions can be taken out by a combination selected from a plurality of constituent elements disclosed. For example, even if several constituent elements are deleted from the entire constituent elements shown in the embodiment, when the problem can be solved and the effect is obtained, the structure in which the constituent elements have been deleted can be taken out as an invention.

10: CMG device 20: Rotating platform mechanism 21: Platform motor 22: Platform axis 23: platform 30: Grinding Stone Support Organization 31: stand 32: Shake the axis 33: Arm 40: Grindstone drive mechanism 41: Rotating motor part 42: Rotation axis 43: Wheel holding member 100: synthetic grindstone 101: Abrasive 102: spherical filler 103: Resin bond M: base material S: gap W: Wafer

Fig. 1 is a perspective view showing a CMG device into which a synthetic grindstone according to an embodiment of the present invention has been incorporated. Fig. 2 is a perspective view showing the synthetic grindstone. Fig. 3 is an explanatory diagram showing the structure of the synthetic grindstone. Fig. 4 is an explanatory diagram showing the synthetic grindstone enlarged by an electron microscope.

100: synthetic grindstone

101: Abrasive

102: spherical filler

103: Resin bond

M: base material

S: gap

W: Wafer

Claims (8)

A synthetic grinding stone, which is used for chemical mechanical grinding of the material to be cut. It has: Abrasive, which has a chemical mechanical grinding effect on the aforementioned material to be cut, and has a particle size of less than 5 μm; Spherical filler, which is formed by a material that is the same or soft as the aforementioned material to be cut or its oxide, and has a larger particle size than the aforementioned abrasive; and The resin bonding agent integrally bonds the aforementioned abrasive and the aforementioned spherical filler. The synthetic grindstone of claim 1, wherein the abrasive is the same or soft material as the material to be cut or its oxide. Such as the synthetic grindstone of claim 1, wherein the volume ratio of the aforementioned abrasive is 0.2-50%, the volume ratio of the aforementioned spherical filler is 20-60%, and the volume of the aforementioned resin bond is 3-25% by volume. Such as the synthetic grindstone of claim 3, wherein the volume ratio of the aforementioned spherical filler is 30-60%. The synthetic grinding stone of claim 1, wherein the aforementioned abrasive is any one or a mixture of silicon dioxide, cerium oxide, chromium oxide, iron oxide, aluminum oxide, and silicon carbide. The synthetic grindstone of claim 1, wherein the aforementioned spherical filler is any one or a mixture of silica, carbon, silica gel, and activated carbon. The synthetic grindstone of claim 1, wherein the aforementioned resin bonding agent is any one or a mixture of thermosetting resin and thermoplastic resin. The synthetic grindstone of claim 1, wherein the material to be cut is mainly composed of silicon, the abrasive is fumed silica, the spherical filler is spherical silica gel, and the resin binder is cellulose.

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